Data Link Connector: Description and Operation

Diagnostic Connector:

Diagnostic Connector (Test Lead Is At Terminal D):

Diagnostic Connector:

Used at the assembly plant to verify proper system operation--prior to shipping the vehicle--the trouble code test lead is located in a connector under the dash.

KEY OFF
Grounding the test lead with the ignition OFF will cause the ECM to display any stored trouble codes.

KEY ON/ENGINE OFF
If the test lead is grounded with the ignition ON and the engine OFF, the ECM will flash a code 12, send a 30 dwell signal to the mixture control solenoid, energize all ECM controlled solenoids and pulse the idle speed control motor in and out.

ENGINE RUNNING
If the test lead is grounded with the engine running, the ECM will function normally except the system will go to closed loop immediately if the engine is warm and the oxygen sensor is hot.

Figure 1 Terminal Arrangement In Connector:

EXTRACTING TROUBLE CODES:
With the ignition switch ON and the engine either stopped or running, the "test" terminal in this connector should be grounded. SEE procedure in TESTING AND INSPECTION.